[Mesa-dev] [PATCH 05/10] intel/fs: Respect CHV/BXT regioning restrictions in copy propagation pass.

[Francisco Jerez]

Iago Toral <itoral at igalia.com> writes:

> On Sat, 2018-12-29 at 12:38 -0800, Francisco Jerez wrote:
>> Currently the visitor attempts to enforce the regioning restrictions
>> that apply to double-precision instructions on CHV/BXT at NIR-to-i965
>> translation time.  It is possible though for the copy propagation
>> pass
>> to violate this restriction if a strided move is propagated into one
>> of the affected instructions.  I've only reproduced this issue on a
>> future platform but it could affect CHV/BXT too under the right
>> conditions.
>> 
>> Cc: mesa-stable at lists.freedesktop.org
>> ---
>>  .../compiler/brw_fs_copy_propagation.cpp      | 10 +++++++
>>  src/intel/compiler/brw_ir_fs.h                | 28
>> +++++++++++++++++++
>>  2 files changed, 38 insertions(+)
>> 
>> diff --git a/src/intel/compiler/brw_fs_copy_propagation.cpp
>> b/src/intel/compiler/brw_fs_copy_propagation.cpp
>> index a8ec1c34630..c23ce1ef426 100644
>> --- a/src/intel/compiler/brw_fs_copy_propagation.cpp
>> +++ b/src/intel/compiler/brw_fs_copy_propagation.cpp
>> @@ -315,6 +315,16 @@ can_take_stride(fs_inst *inst, unsigned arg,
>> unsigned stride,
>>     if (stride > 4)
>>        return false;
>>  
>> +   /* Bail if the channels of the source need to be aligned to the
>> byte offset
>> +    * of the corresponding channel of the destination, and the
>> provided stride
>> +    * would break this restriction.
>> +    */
>> +   if (has_dst_aligned_region_restriction(devinfo, inst) &&
>> +       !(type_sz(inst->src[arg].type) * stride ==
>> +           type_sz(inst->dst.type) * inst->dst.stride ||
>> +         stride == 0))
>> +      return false;
>> +
>>     /* 3-source instructions can only be Align16, which restricts
>> what strides
>>      * they can take. They can only take a stride of 1 (the usual
>> case), or 0
>>      * with a special "repctrl" bit. But the repctrl bit doesn't work
>> for
>> diff --git a/src/intel/compiler/brw_ir_fs.h
>> b/src/intel/compiler/brw_ir_fs.h
>> index 07e7224e0f8..95b069a2e02 100644
>> --- a/src/intel/compiler/brw_ir_fs.h
>> +++ b/src/intel/compiler/brw_ir_fs.h
>> @@ -486,4 +486,32 @@ get_exec_type_size(const fs_inst *inst)
>>     return type_sz(get_exec_type(inst));
>>  }
>>  
>> +/**
>> + * Return whether the following regioning restriction applies to the
>> specified
>> + * instruction.  From the Cherryview PRM Vol 7. "Register Region
>> + * Restrictions":
>> + *
>> + * "When source or destination datatype is 64b or operation is
>> integer DWord
>> + *  multiply, regioning in Align1 must follow these rules:
>> + *
>> + *  1. Source and Destination horizontal stride must be aligned to
>> the same qword.
>> + *  2. Regioning must ensure Src.Vstride = Src.Width * Src.Hstride.
>> + *  3. Source and Destination offset must be the same, except the
>> case of
>> + *     scalar source."
>> + */
>> +static inline bool
>> +has_dst_aligned_region_restriction(const gen_device_info *devinfo,
>> +                                   const fs_inst *inst)
>> +{
>> +   const brw_reg_type exec_type = get_exec_type(inst);
>> +   const bool is_int_multiply =
>> !brw_reg_type_is_floating_point(exec_type) &&
>> +         (inst->opcode == BRW_OPCODE_MUL || inst->opcode ==
>> BRW_OPCODE_MAD);
>
> Should this be extended to include MAC and MACH too?
>

The documentation is unclear, but it doesn't look like that's the case
according to the simulator, because those instructions don't do more
than a 16x16 or 32x16 bit integer multiply respectively.

>> +
>> +   if (type_sz(inst->dst.type) > 4 || type_sz(exec_type) > 4 ||
>> +       (type_sz(exec_type) == 4 && is_int_multiply))
>> +      return devinfo->is_cherryview ||
>> gen_device_info_is_9lp(devinfo);
>
> How about:
>
> if (devinfo->is_cherryview || gen_device_info_is_9lp(devinfo)) {
>    ...
> } else {
>    return false;
> }
>
> since we only really need to do these checks in those platforms it
> might make a bit more sense to do it this way.
>

Right now the difference is purely cosmetic, but in the future that
won't work for the platform this was designed for, I can send you more
details off-list.

>> +   else
>> +      return false;
>> +}
>> +
>>  #endif
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